High density aqueous well fluids

ABSTRACT

This invention provides zinc-free aqueous brine compositions. These zinc-free aqueous brine compositions have a density of about 14.3 pounds per gallon or more, and a true crystallization temperature of about 20° F. or less, and comprise water and one or more inorganic bromide salts, with the provisos that
         when calcium bromide is present, one or more other water-soluble inorganic salts are also present,   when lithium bromide is present, calcium bromide is absent,   when bismuth(III) bromide is present, one or more other water-soluble inorganic salts are also present, and   for a true crystallization temperature of about 10° F. or less, when manganese(II) bromide is present, one or more other water-soluble inorganic salts are also present.
 
Processes for forming these zinc-free aqueous brine compositions are also provided.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/502,914, filed Feb. 9, 2017, which application is the National Phaseof International Patent Application PCT/US2015/041662, filed on Jul. 23,2015, which application claims priority from U.S. Application No.62/185,171, filed Jun. 26, 2015; U.S. Application No. 62/103,668 filedJan. 15, 2015; and U.S. Application No. 62/036,912 filed Aug. 13, 2014,the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to high density aqueous brines suitable for useas well fluids.

BACKGROUND

Conventional aqueous brine fluids, like calcium bromide, which can havedensities up to about 14.2 pounds per gallon (1.70 kg/L), are widelyused in oilfield production as clear completion fluids, drilling fluids,packer fluids, and so forth. For some wells, downhole pressures canreach 30,000 psi (2.1×10⁸ Pa). Such high pressures occur downhole atleast in the Gulf of Mexico, and temperatures at the mud line in theGulf of Mexico can reach 40° F. (4.4° C.). As a general observation,each 10,000 pounds per square inch (6.9×10⁷ Pa) increase in pressure canincrease the crystallization temperature of an aqueous brine by aboutten Fahrenheit degrees (about 5.6 Celsius degrees).

Typical aqueous brine fluids include calcium bromide having densities upto about 14.2 ppg (1.70 kg/L). A calcium bromide aqueous brine of about14.2 ppg (1.70 kg/L) density has a true crystallization temperature of10° F. (−12.2° C.). Calcium bromide aqueous brines having densities ashigh as 15 ppg (1.8 kg/L) can be made; however, these solutions have atrue crystallization temperature of about 61° F. (16.1° C.). Thesehigher density calcium bromide aqueous brines are not suitable for usein some downhole applications, such as conditions often found in theGulf of Mexico, because precipitates will form in these higher densitycalcium bromide aqueous brines due to their relatively high truecrystallization temperatures.

Zinc-containing calcium bromide aqueous brines of high density, e.g.,about 14.5 pounds per gallon (1.74 kg/L) or greater, are easily obtainedby blending enough zinc bromide into the calcium bromide aqueous brineto reach the desired density value. Zinc-containing calcium bromideaqueous brines have true crystallization temperatures that are usuallyabout 20° F. (−6.7° C.) or lower, making these zinc-containing brinesmore suitable for downhole use. However, inclusion of zinc necessitatesincreased reporting to government agencies for environmental reasons,resulting in more costly environmental mitigation measures. For example,zinc is regulated as a Priority Pollutant by the United StatesEnvironmental Protection Agency (EPA).

Hence, there is a need to develop high density aqueous brine fluids thatare zinc-free, and that have true crystallization temperatures that aresuitably low for downhole use.

SUMMARY OF THE INVENTION

This invention provides aqueous brines of high density and lowcrystallization temperature that are zinc-free. It has been discovered,for example, that a high density, zinc-free aqueous brine can beprepared from a combination of water and one or more inorganic bromidesalts such as calcium bromide, manganese bromide (MnBr₂) tin bromide(SnBr₂ or SnBr₄), bismuth bromide, and/or indium bromide; calciumbromide is used in combination with one or more other water-solubleinorganic salts, preferably selected from an inorganic bromide salt,manganese(II) nitrate, and a water-soluble polytungstate salt; lithiumbromide is used in combination with an alkali metal polytungstate salt;bismuth(III) bromide is used in combination with one or more otherwater-soluble inorganic salts, preferably selected from an inorganicbromide salt; when lithium bromide is present, calcium bromide isabsent. Such brines can exhibit densities of about 15.0 ppg (1.78 kg/L)or greater, and have crystallization temperatures of about 20° F. (−6.7°C.) or less, often about 10° F. (−12.2° C.) or less. These brines aresuitable for use as wellbore fluids, such as completion fluids,especially clear completion fluids, drilling fluids, packer fluids,workover fluids, and other fluids that employ aqueous brines,particularly aqueous brines of high density. The aqueous brines of thisinvention are well suited for offshore completion activities involvinghigh pressure reservoirs, such as oil and gas fields located in the Gulfof Mexico.

An embodiment of this invention is a zinc-free aqueous brinecomposition. The composition has a density of about 14.3 pounds pergallon (1.71 kg/L) or more, and a true crystallization temperature ofabout 20° F. (−6.7° C.) or less, preferably about 10° F. (−12.2° C.) orless, and comprises water and one or more inorganic bromide salts, withthe proviso that when calcium bromide is present, one or more otherwater-soluble inorganic salts is also present, preferably selected froman inorganic bromide salt, manganese(II) nitrate, and a water-solublepolytungstate salt; with the proviso that when bismuth(III) bromide ispresent, one or more other water-soluble inorganic salts is alsopresent, preferably selected from an inorganic bromide salt, with theproviso that when lithium bromide is present, calcium bromide is absent,and with the proviso that for true crystallization temperatures of about10° F. or less, when manganese(II) bromide is present, one or more otherwater-soluble inorganic salts are also present. Processes for formingthese aqueous brine compositions are also provided.

These and other embodiments and features of this invention will be stillfurther apparent from the ensuing description and appended claims.

FURTHER DETAILED DESCRIPTION OF THE INVENTION

As used throughout this document, the phrase “zinc-free” means thatexcept for adventitious impurities, neither zinc nor zinc compounds arepresent in, or introduced into, the compositions or processes of thisinvention. Generally, there is about 25 ppm or less of zinc present inthe aqueous brines of this invention.

The term ppm means parts per million (wt/wt), as used throughout thisdocument, unless specifically stated otherwise herein. Throughout thisdocument, both “ppg” and “lb/gal” are abbreviations for pounds pergallon.

The abbreviation “TCT” stands for true crystallization temperature (ortrue crystallization point) as used throughout this document. Truecrystallization temperature is the temperature at which precipitatebegins to form in the absence of supercooling. A method for determiningtrue crystallization temperature is described hereinbelow.

The phrases “inorganic bromide salt”, “inorganic bromide”, and “bromidesalt” are used interchangeably throughout this document.

Solutions comprising one or more inorganic bromide salts andmanganese(II) nitrate or a water-soluble polytungstate are aqueousbrines of the present invention.

Because the compositions of the invention can be used as clearcompletion fluids, precipitates and/or cloudiness in the aqueous brinesof the invention are undesirable. To be suitable for use as well fluids,the aqueous brines of the invention have little or no precipitateformation over time (e.g., about one week) at ambient temperature andpressure (e.g., 17 to 25° C. and 14 to 15 psi) or at elevatedtemperature (e.g., about 60° C.) and ambient pressure.

The compositions of the invention are aqueous brine solutions comprisingone or more inorganic bromide salts other than zinc bromide. Although itis convenient to refer to compounds of bromide salts and to metalcations and bromide anions, the species in the compositions may becomplexed with water, or in some other form. Similarly, the otherwater-soluble inorganic salts which are comprised in the aqueous brinesolutions of the invention that are referred to as salts or theirrespective cations and/or anions may be complexed with water, or in someother form.

In the practice of this invention, the inorganic bromide salts areselected from calcium bromide, manganese(II) bromide, tin(II) bromide,tin(IV) bromide, bismuth(III) bromide, indium(III) bromide, and mixturesof any two or more of these; when calcium bromide is used, one or moreother water-soluble inorganic salts is also used, and preferably isselected from an inorganic bromide salt, manganese(II) nitrate, and awater-soluble polytungstate salt; when bismuth(III) bromide is used, oneor more other water-soluble inorganic salts is also used, and preferablyis selected from an inorganic bromide salt. Manganese(II) bromide ispreferably used in combination with one or more other water-solubleinorganic salts, especially when a brine with a true crystallizationtemperature of about 10° F. (−12.2° C.) or less is needed; in preferredembodiments, the other inorganic salt is preferably selected from aninorganic bromide salt, manganese(II) nitrate, and a water-solublepolytungstate salt, more preferably an inorganic bromide, whichinorganic bromide is preferably calcium bromide or a combination ofcalcium bromide and one or more other inorganic bromide salts. In someembodiments, the inorganic bromide salt is lithium bromide incombination with an alkali metal polytungstate salt. Preferred inorganicbromide salts when only one bromide salt is present include tin(IV)bromide and indium(III) bromide, especially tin(IV) bromide. When twobromide salts are used, they are preferably a combination of calciumbromide and manganese(II) bromide; when three bromide salts are used,they are preferably a combination of calcium bromide, manganese(II)bromide and tin(IV) bromide, or a combination of calcium bromide,manganese(II) bromide, and bismuth(III) bromide.

In some preferred embodiments, the inorganic bromide salt ismanganese(II) bromide, tin(II) bromide, tin(IV) bromide, indium(III)bromide, or a mixture of any two or more of these. In other preferredembodiments, the inorganic bromide salt is a combination of calciumbromide and one or more inorganic bromide salts selected frommanganese(II) bromide, tin(II) bromide, tin(IV) bromide, bismuth(III)bromide, indium(III) bromide, or a mixture of any two or more of these.In another preferred embodiment, the inorganic bromide salt is acombination of bismuth(III) bromide and one or more inorganic bromidesalts selected from manganese(II) bromide, tin(II) bromide, tin(IV)bromide, indium(III) bromide, or a mixture of any two or more of these.In still another preferred embodiment, one inorganic bromide salt ispresent, and the inorganic bromide salt is tin(IV) bromide orindium(III) bromide.

When the other water-soluble inorganic salt is a water-solublepolytungstate salt, it can be an alkali metal polytungstate, an alkalineearth metal polytungstate, manganese polytungstate, and the like. Alkalimetal polytungstates include lithium polytungstate, lithiummetatungstate, sodium polytungstate, sodium metatungstate, potassiumpolytungstate, potassium metatungstate, and the like; preferred alkalimetal polytungstates include sodium metatungstate and potassiummetatungstate. Alkaline earth metal polytungstates include calciumpolytungstate, magnesium polytungstate, and strontium polytungstate;preferred alkaline earth polytungstates include calcium polytungstate.The term “metatungstate” often refers to a hydrated form of apolytungstate salt.

For the combination of lithium bromide with an alkali metalpolytungstate salt, the alkali metal polytungstate salts include lithiumpolytungstate, lithium metatungstate, sodium polytungstate, sodiummetatungstate, potassium polytungstate, potassium metatungstate, and thelike; preferred alkali metal polytungstates include lithiummetatungstate and sodium metatungstate.

When the inorganic salts of the aqueous brine are comprised only ofinorganic bromide salts, the total amount of inorganic bromide salt(s)in the aqueous brine is typically in the range of about 40 wt % to about75 wt %, relative to the total weight of the composition. Preferredtotal amounts of inorganic bromide salt(s) are from about 45 wt % toabout 75 wt %, relative to the total weight of the composition.

In some embodiments, the total amount of inorganic bromide salt(s) inthe aqueous brine is preferably in the range of about 45 wt % to about65 wt %, more preferably about 55 wt % to about 65 wt %, relative to thetotal weight of the composition, especially when calcium bromide and oneother inorganic bromide salt are used, and the other inorganic bromidesalt is selected from tin(II) bromide, tin(IV) bromide, bismuth(III)bromide, and indium(III) bromide.

In other embodiments, the total amount of inorganic bromide salt(s) inthe aqueous brine is preferably in the range of about 55 to about 70 wt%, relative to the total weight of the composition, especially when theinorganic bromide salts are calcium bromide and two other inorganicbromide salts, which other inorganic bromide salts are a combination ofmanganese(II) bromide and one other metal bromide selected from tin(II)bromide, tin(IV) bromide, bismuth(III) bromide, and indium(III) bromide.

When the inorganic salts of the aqueous brine are comprised of one ormore inorganic bromide salts and one or more other water-solubleinorganic salts, the total amount of inorganic bromide salt(s) in theaqueous brine is typically in the range of about 15 wt % to about 60 wt%, preferably about 20 wt % to about 55 wt %, more preferably about 25wt % to about 55 wt %, relative to the total weight of the composition.The total amount of the other water-soluble inorganic salt(s) varies,depending on the identity of the inorganic salt. For manganese(II)nitrate, the total amount in the aqueous brine is usually in the rangeof about 5 wt % to about 75 wt %, sometimes preferably about 35 wt % toabout 70 wt %, sometimes preferably about 10 wt % to about 50 wt %,relative to the total weight of the composition; for water-solublepolytungstate salts, the total amount in the aqueous brine is typicallyin the range of about 5 wt % to about 40 wt %, preferably about 10 wt %to about 35 wt %, relative to the total weight of the composition.

The total amount of inorganic salts in an aqueous brine comprised of oneor more inorganic bromide salts and one or more other water-solubleinorganic salts is in the range of about 60 wt % to about 85 wt %,sometimes preferably in the range of about 65 wt % to about 85 wt %,relative to the total weight of the composition when the otherwater-soluble inorganic salt is manganese(II) nitrate. When the otherwater-soluble inorganic salt is a water-soluble polytungstate, the totalamount of inorganic salts in an aqueous brine comprised of one or moreinorganic bromide salts and one or more other water-soluble inorganicsalts is in the range of about 50 wt % to about 75 wt %, preferably inthe range of about 55 wt % to about 70 wt %, relative to the totalweight of the composition.

Compositions of the invention have densities of about 14.3 pounds pergallon (1.71 kg/L) or more. Preferably, the compositions have densitiesof about 14.6 ppg (1.75 kg/L) or more. In some embodiments, thecompositions preferably have densities of about 14.8 ppg (1.77 kg/L) ormore, or preferably about 15.0 ppg (1.80 kg/L) or more, or morepreferably about 15.1 ppg (1.81 kg/L) or more. In other embodiments,especially when the inorganic bromide salt is calcium bromide and one ormore inorganic bromide salts selected from tin(IV) bromide, bismuth(III)bromide, or indium(III) bromide, the compositions preferably havedensities of about 16.0 ppg (1.92 kg/L) or more.

Density ranges for the compositions of this invention are preferablyabout 14.3 ppg (1.71 kg/L) to about 19.0 ppg (2.28 kg/L), morepreferably about 14.6 ppg (1.75 kg/L) to about 18.0 ppg (2.16 kg/L). Insome embodiments, preferred densities are about 14.8 ppg (1.77 kg/L) toabout 16.0 ppg (1.92 kg/L), more preferably about 15.0 ppg (1.80 kg/L)to about 16.0 ppg (1.92 kg/L), and still more preferably about 15.1 ppg(1.81 kg/L) to about 15.6 ppg (1.87 kg/L). In other embodiments,preferred densities are about 14.6 ppg (1.75 kg/L) to about 15.0 ppg(1.80 kg/L), more preferably about 14.6 to about 14.8 ppg (1.77 kg/L).In still other embodiments, preferred densities are about 15.0 ppg (1.80kg/L) to about 18.0 ppg (2.16 kg/L), more preferably about 15.5 ppg(1.86 kg/L) to about 17.75 ppg (2.13 kg/L). In yet other embodiments,especially when the inorganic bromide salt is calcium bromide and oneother inorganic bromide salt selected from tin(IV) bromide, bismuth(III)bromide, or indium(III) bromide, preferred densities are about 16.0 ppg(1.92 kg/L) to about 17.5 ppg (2.10 kg/L), more preferably about 16.2ppg (1.94 kg/L) to about 17.2 ppg (2.06 kg/L). In another embodiment,especially when the inorganic bromide salt is calcium bromide andmanganese(II) nitrate is the other water-soluble inorganic salt,preferred densities are about 14.5 ppg (1.74 kg/L) to about 16.0 ppg(1.92 kg/L). In yet another embodiment, preferred densities are about14.5 ppg (1.74 kg/L) to about 17.5 ppg (2.10 kg/L), more preferablyabout 14.5 ppg (1.74 kg/L) to about 16.5 ppg (1.98 kg/L), especiallywhen the inorganic bromide salt is calcium bromide or manganese(II)bromide and the other water-soluble inorganic salt is a water-solublepolytungstate salt, or when the inorganic bromide salt is lithiumbromide in combination with an alkali metal polytungstate salt.

For the compositions of the invention, the true crystallizationtemperatures are generally about 20° F. (−6.7° C.) or less, preferablyabout 10° F. (−12.2° C.) or less, more preferably about 8° F. (−13.3°C.) or less, and still more preferably about 7.5° F. (−13.6° C.) orless.

Aqueous brine compositions of the invention normally have pH values ofabout −2 or more, and can range from about −2 to about 8. Preferred pHvalues are in the range of about 0 to about 7; more preferred are pHvalues in the range of about 1 to about 6; still more preferred are pHvalues in the range of about 1.5 to about 5, especially about 2.5 toabout 5. Even more preferred are pH values in the range of about 3 toabout 4.

As is known in the art, it is often useful to include one or moreoptional additives in an aqueous brine, and the inclusion of suchadditives is within the scope of this invention. Optional additives caninclude, for example, corrosion inhibitors, lubricants, pH controladditives, surfactants, and/or solvents. Glycerol and formic acid arepreferred optional additives.

In some preferred zinc-free aqueous brine compositions of the invention,only water, inorganic bromide salts, one or more other water-solubleinorganic salts, and species derived from these components are presentin the composition; in some of these preferred embodiments, one of theinorganic bromide salts is calcium bromide. In some of these preferredembodiments, the other water-soluble inorganic salts are selected frommanganese(II) nitrate, and a water-soluble polytungstate salt, and morepreferably, one of the inorganic bromide salts is calcium bromide.

In other preferred zinc-free aqueous brine compositions of theinvention, only water, inorganic bromide salts, and species derived fromthese components are present in the composition; in some of thesepreferred embodiments, one of the inorganic bromide salts is calciumbromide. In other preferred zinc-free aqueous brine compositions of theinvention, only water, tin(IV) bromide, and species derived from thesecomponents are present in the composition.

Preferred compositions of this invention include zinc-free aqueousbrines which comprise water; calcium bromide; and one or more otherinorganic bromide salts, preferably selected from manganese(II) bromide,tin(II) bromide, tin(IV) bromide, bismuth(III) bromide, indium(III)bromide, and mixtures of any two or more of these; wherein thecomposition has a density of about 14.3 ppg (1.71 kg/L) or more,preferably about 14.6 ppg (1.75 kg/L) or more, more preferably about15.0 ppg (1.80 kg/L) or more; and a true crystallization temperature ofabout 20° F. (−6.7° C.) or less, preferably about 10° F. (−12.2° C.) orless, more preferably about 8° F. (−13.3° C.) or less. In these calciumbromide-containing compositions, the inorganic bromide salt(s) otherthan calcium bromide is preferably in an amount of about 3.0 wt % toabout 40 wt %, relative to the total weight of the composition;preferably, these calcium bromide-containing compositions have a pH inthe range of about 0 to about 8, more preferably about 1 to 7.

Additional preferred compositions of this invention include zinc-freeaqueous brines which comprise water and one inorganic bromide saltselected from tin(IV) bromide and indium(III) bromide; more preferablytin(IV) bromide; wherein the composition has a density of about 15.0 ppg(1.80 kg/L) or more, preferably about 16.0 ppg (1.92 kg/L) or more, morepreferably about 18.0 ppg (2.16 kg/L) or more.

In a preferred embodiment, the inorganic bromide salts are calciumbromide and manganese(II) bromide, and the composition has a density ofabout 14.6 ppg (1.75 kg/L) or more and a true crystallizationtemperature at atmospheric pressure of about 20° F. (−6.7° C.) or less,preferably about 10° F. (−12.2° C.) or less. Particularly preferred arecompositions containing calcium bromide and manganese(II) bromide whichhave densities of about 15 lb/gal (1.8 kg/L) or more, and truecrystallization temperatures at atmospheric pressure of about 8° F.(−13.3° C.) or less. Preferably, these compositions containing calciumbromide and manganese(II) bromide have pH values in the range of about2.5 to 5, more preferably about 3 to 4.

In some preferred embodiments, the inorganic bromide salts are calciumbromide and manganese(II) bromide in combination with another inorganicbromide salt selected from tin(IV) bromide, tin(II) bromide,bismuth(III) bromide, and indium(III) bromide.

In another preferred embodiment, the inorganic bromide salts are calciumbromide, manganese(II) bromide, and tin(IV) bromide, and the compositionhas a density of about 15.0 ppg (1.80 kg/L) or more. Particularlypreferred compositions containing calcium bromide, manganese(II)bromide, and tin(IV) bromide as the inorganic bromide salts havedensities of about 16.0 ppg (1.92 kg/L) or more, more preferablydensities of about 16.5 ppg (1.98 kg/L) or more.

In still another preferred embodiment, the inorganic bromide salts arecalcium bromide, manganese(II) bromide, and bismuth(III) bromide, andthe composition has a density of about 16.0 ppg (1.92 kg/L) or more.Particularly preferred compositions containing calcium bromide,manganese(II) bromide, and bismuth(III) bromide as the inorganic bromidesalts have densities of about 16.3 ppg (1.95 kg/L) or more.

In another preferred embodiment, the inorganic bromide salt is calciumbromide, and manganese(II) nitrate is present; preferably, thecomposition has a density of about 14.5 ppg (1.74 kg/L) or more, morepreferably about 14.8 ppg (1.77 kg/L) or more.

In yet another preferred embodiment, the inorganic bromide salt iscalcium bromide or manganese(II) bromide, and a water-solublepolytungstate, preferably an alkali metal polytungstate, more preferablysodium metatungstate, is present; more preferably, the composition has adensity of about 14.5 ppg (1.74 kg/L) or more, more preferably about14.8 ppg (1.77 kg/L) or more.

In a further preferred embodiment, the inorganic bromide salt is lithiumbromide in combination with an alkali metal polytungstate salt; morepreferably the alkali metal polytungstate salt is lithium metatungstateor sodium metatungstate; more preferably, the composition has a densityof about 14.5 ppg (1.74 kg/L) or more, more preferably about 14.8 ppg(1.77 kg/L) or more.

Zinc-free aqueous brines having a density of about 14.3 pounds pergallon (1.71 kg/L) or more and a true crystallization temperature ofabout 20° F. (−6.7° C.) or less are formed by processes which comprisecombining, in any order, components comprising water and one or moreinorganic bromide salts, with the proviso that when calcium bromide ispresent, one or more other water-soluble inorganic salts is alsopresent, and preferably is selected from an inorganic bromide salt,manganese(II) nitrate, and a water-soluble polytungstate salt; with theproviso that when lithium bromide is present, calcium bromide is absent;with the proviso that when bismuth(III) bromide is present, one or moreother water-soluble inorganic salts are also present; and with theproviso that, for a true crystallization temperature of about 10° F. orless, when manganese(II) bromide is present, one or more otherwater-soluble inorganic salts are also present.

The inorganic bromide salt(s) include calcium bromide, manganese(II)bromide, tin(II) bromide, tin(IV) bromide, bismuth(III) bromide,indium(III) bromide, and mixtures of any two or more of these. Whencalcium bromide is used, one or more other water-soluble inorganicsalts, preferably selected from an inorganic bromide salt, manganese(II)nitrate, and a water-soluble polytungstate salt, is also used. Whenbismuth(III) bromide is used, one or more other water-soluble inorganicsalts, preferably selected from an inorganic bromide salt, is also used.When lithium bromide is used, an alkali metal polytungstate salt is alsoused. Manganese(II) bromide is preferably used in combination with oneor more other water-soluble inorganic salts, especially when a brinewith a true crystallization temperature of about 10° F. (−12.2° C.) orless is needed; in preferred embodiments, the other inorganic salt is aninorganic bromide, manganese(II) nitrate, or a water-solublepolytungstate salt; the inorganic bromide is preferably calcium bromideor a combination of calcium bromide and one or more other inorganicbromide salts. When one inorganic bromide salt is used, it is preferablytin(IV) bromide or indium(III) bromide, more preferably, tin(IV)bromide. Manganese(II) bromide is preferred as an inorganic bromide saltto use with calcium bromide, especially when calcium bromide and oneother bromide salt are present; when two bromide salts are used withcalcium bromide, they are preferably a combination of manganese(II)bromide and tin(IV) bromide, or a combination of manganese(II) bromideand bismuth(III) bromide.

The combining of the water and inorganic bromide salt(s), and, whenused, other water-soluble inorganic salts can be conducted in any mannerused to mix inorganic salts and water. Normally and preferably,concentrated solutions of the inorganic salts can be mixed with additionor removal of water to provide the composition desired. Alternatively,the inorganic bromide salt(s) are added to the water. When there are twoor more inorganic bromide salts, the inorganic bromide salts can bemixed with a portion of water before being combined with each other and,if needed, more water. When cofeeding the components or mixturesthereof, there is no requirement that the feeds be entirely co-extensivein time, and each feed may be interrupted at one or more points duringthe cofeeding. Another preferred way of operating when there are two ormore inorganic bromide salts is to introduce one or more of theinorganic bromide salt(s) as a solid into a preformed aqueous solutionof the other inorganic bromide salts(s). A combination of methods can beused as desired.

One or more of the inorganic bromide salts can be formed during theprocess. Formation of an inorganic bromide salt during the process canbe used to form a portion of, or all of, the inorganic bromide salt.When an inorganic bromide salt is formed during the process, it can beformed in water before some or all of any other inorganic bromide(s) areintroduced, or, preferably, in an aqueous solution of the otherinorganic bromide(s).

An inorganic bromide salt can be formed during the process in variousways. In some embodiments, an inorganic bromide salt can be formed fromthe metal in elemental form and elemental bromine (Bra), especiallywhere the metal is calcium, manganese, tin, bismuth, and/or indium. Forexample, manganese metal and elemental bromine can be used to formmanganese(II) bromide. In other embodiments, an inorganic bromide saltcan be formed from an inorganic oxide and/or hydroxide and a bromidesource which is hydrogen bromide and/or elemental bromine. In preferredembodiments, the inorganic bromide salt is formed from (i) an inorganicoxide and/or hydroxide and (ii) hydrogen bromide and/or bromine.

Inorganic oxides and/or hydroxides that can be used to form an inorganicbromide salt during the process include one or more of calcium oxideand/or hydroxide, manganese oxides and/or hydroxides, tin(II) oxideand/or hydroxide, tin(IV) oxide and/or hydroxide, bismuth(III) oxideand/or hydroxide, indium(III) oxide and/or hydroxide, or mixtures of anytwo or more of the foregoing. Preferred inorganic oxides and hydroxidesinclude one or more manganese oxides and/or hydroxides, tin(IV) oxideand/or hydroxide, and bismuth(III) oxide and/or hydroxide. Of themanganese oxides and/or hydroxides, more preferred are manganese(II)oxide, manganese(II) hydroxide, and mixtures thereof; even morepreferred is manganese(II) oxide.

When one or more inorganic oxides and/or hydroxides are used, thebromide source for forming an inorganic bromide during the process ishydrogen bromide, bromine, or a mixture thereof. Preferably, the bromidesource is hydrogen bromide or a mixture of hydrogen bromide and bromine;more preferred is a mixture of hydrogen bromide and bromine. In thesemixtures, the hydrogen bromide and bromine can be in any desiredproportions from 100% hydrogen bromide to 100% Br₂, or at any relativeproportion therebetween. For convenience, it may be preferable to employa mixture in which hydrogen bromide is present. When bromine (elementalbromine, Br₂) is used, either alone or in admixture with hydrogenbromide, a reducing agent is also present, and is typically methanol,ethanol, formic acid, hydrazine, and the like.

For the combination of lithium bromide and an alkali metal polytungstatesalt, the lithium bromide can be made by any of the methods describedabove, including from lithium metal and elemental bromine, and fromlithium oxide and/or hydroxide and a bromide source (typically hydrogenbromide or elemental bromine).

In some preferred processes, the inorganic bromide salt is manganese(II)bromide, tin(II) bromide, tin(IV) bromide, indium(III) bromide, or amixture of any two or more of these. In other preferred processes, theinorganic bromide salt is a combination of calcium bromide andmanganese(II) bromide, tin(II) bromide, tin(IV) bromide, bismuth(III)bromide, indium(III) bromide, or a mixture of any two or more of these.In another preferred embodiment, a combination of bismuth(III) bromideand manganese(II) bromide, tin(II) bromide, tin(IV) bromide, indium(III)bromide, or a mixture of any two or more of these, is used. In stillanother embodiment, only one inorganic bromide salt is used, and theinorganic bromide salt is tin(IV) bromide or indium(III) bromide.

When one inorganic bromide salt is used to form a zinc-free aqueousbrine of the invention, the inorganic bromide is typically in an amountin the range of about 40 wt % to about 75 wt %, preferably about 45 wt %to about 75 wt %, relative to the total weight of the aqueous brinecomposition being formed. When there are two or more inorganic bromidesalts, this range refers to the combined weight of all of the inorganicbromide salts. When the composition contains calcium bromide, preferredamounts of inorganic bromide salts other than the calcium bromide in theaqueous brine are from about 5 wt % to about 35 wt %; more preferablyabout 6 wt % to about 30 wt %, relative to the total weight of thecomposition.

When an inorganic bromide and one or more other water-soluble inorganicsalts are used to form a zinc-free aqueous brine of the invention,especially manganese(II) nitrate or a water-soluble polytungstate salt,the inorganic bromide is typically about 15 wt % to about 60 wt %,preferably about 20 wt % to about 55 wt %, more preferably about 25 wt %to about 55 wt %, relative to the total weight of the composition. Whenthe other water-soluble inorganic salt is manganese(II) nitrate, themanganese(II) nitrate is generally in the range of about 5 wt % to about75 wt %, sometimes preferably about 35 wt % to about 70 wt %, sometimespreferably about 10 wt % to about 50 wt %, relative to the total weightof the composition. When the other water-soluble inorganic salt is awater-soluble polytungstate salt, the polytungstate salt is usually inthe range of about 5 wt % to about 40 wt %, preferably about 10 wt % toabout 35 wt %, relative to the total weight of the composition.

When an inorganic bromide salt is formed during the process, the amountof that inorganic bromide salt is calculated as if the inorganic bromidesalt had been added. Amounts of inorganic bromide salt will vary,depending to some extent on the amount(s) of other inorganic bromide(s),because less inorganic bromide salt is needed to reach a particulardensity value as the amount of other inorganic bromide salt(s)increases.

In some embodiments, when forming a zinc-free aqueous brine of theinvention, the amount of inorganic bromide salt in the aqueous brine ispreferably in the range of about 45 wt % to about 65 wt %, morepreferably about 55 wt % to about 65 wt %, relative to the total weightof the composition, especially when calcium bromide and one otherinorganic bromide salt are used, and the other inorganic bromide salt isselected from tin(II) bromide, tin(IV) bromide, bismuth(III) bromide,and indium(III) bromide.

In other embodiments, when forming a zinc-free aqueous brine of theinvention, the amount of inorganic bromide salt in the aqueous brine ispreferably in the range of about 55 to about 70 wt %, relative to thetotal weight of the composition, especially when the inorganic bromidesalts are calcium bromide and two other inorganic bromide salts, whichare a combination of manganese(II) bromide and another metal bromideselected from tin(II) bromide, tin(IV) bromide, bismuth(III) bromide,and indium(III) bromide.

The amount of water and/or the inorganic bromide salt(s) and/or otherwater-soluble inorganic salt(s) used to form the aqueous brines of theinvention can be adjusted to reach the desired density. Removal ofwater, for example by heating and/or applying a vacuum, can be employedto reach the desired density for the zinc-free aqueous brinecomposition.

The zinc-free aqueous brine can be heated during combination of thecomponents and/or after the components are combined, to ensuredissolution of the components. In this optional heating step, themixture being formed during the process and/or the aqueous brine formedby the process is heated at a temperature of about 40° C. or above toform a heated solution. Elevated temperatures can increase the rate ofdissolution of the inorganic bromide salt(s). Such elevated temperaturesfor heating the aqueous brine are typically in the range of about 40° C.up to the boiling point of the mixture, preferably about 45° C. to about100° C., more preferably about 50° C. to about 95° C., and still morepreferably about 60° C. to about 95° C. In some embodiments, it ispreferred to operate under increased pressure, typically about 20 psi toabout 40 psi (1.4×10⁵ to 2.77×10⁵ Pa), because higher temperatures canbe achieved. Upon cooling the aqueous brine to ambient temperatures(typically about 15° C. to about 25° C., often about 17° C. to about 23°C.), the inorganic bromide salt(s) usually remain dissolved.

Optionally, the pH of the zinc-free aqueous brine can be adjusted byadding an acid or a base as needed. Suitable acids include mineral acidsand water-soluble organic acids; suitable bases are usually inorganicoxides and/or hydroxides. In some instances, upon introduction of aninorganic oxide and/or hydroxide to the zinc-free aqueous brine, aprecipitate may form; after filtration, a clear aqueous brine isobtained.

For pH adjustment, suitable inorganic oxides and hydroxides whichinclude oxides and hydroxides of manganese(II), tin(II), tin(IV),bismuth(III), indium(III), alkali metals including lithium, sodium, andpotassium, alkaline earth metals including calcium and magnesium, andmixtures of any of these oxides and/or hydroxides, may be used.Preferred inorganic oxides and hydroxides include those of manganese,tin, calcium, and sodium. In some preferred embodiments, the inorganicoxide(s) and/or hydroxide(s) has one or more of the same cations alreadypresent in the aqueous brine. In some embodiments, a small amount ofprecipitate forms when an inorganic oxide and/or hydroxide is used toincrease the pH. Once the precipitate has been removed, e.g., byfiltration, additional precipitate formation usually does not occur.

Acids suitable for pH adjustment include mineral acids and organic acidsthat are water-soluble. Suitable mineral acids include hydrogenchloride, hydrogen bromide, hydrogen iodide, nitric acid, sulfuric acid,phosphoric acid, and the like. Suitable organic acids include formicacid, tartaric acid, citric acid, gluconic acid, lactic acid, malicacid, maleic acid, malonic acid, oxalic acid, and the like. Mixtures ofany two or more acids can be employed if desired. Hydrogen bromide is apreferred acid, and can be used in gaseous form, or, preferably, as anaqueous solution.

Any optional additives that are included in the aqueous brines can beintroduced in any of the ways that the inorganic bromide salt(s) areintroduced, or in any other convenient manner.

Under storage conditions, aqueous brines having a density of about 15.0ppg (1.80 kg/L) or greater often form a precipitate. Stabilization ofthese dense aqueous brines can be achieved by adjusting the pH of theaqueous brine. Adjustment of the pH value is accomplished by adding aninorganic hydroxide and/or oxide and/or by adding an acid, preferablyhydrogen bromide, usually to a value in the range of about 1 to about 7,more preferably about 1 to about 6; still more preferably about 2.5 toabout 5.

Small amounts of fine precipitates are sometimes formed in aqueous brinecompositions of the invention which have a pH of about 3.5 or higher,and in which the inorganic bromide salts are calcium bromide andmanganese(II) bromide. In particular, it has been discovered thatdecreasing the pH of the aqueous brine compositions may minimize orprevent further precipitate formation in the aqueous brine. In suchinstances, the pH can be adjusted as described above.

In some embodiments of this invention, the presence of glycerol and/orformic acid in the composition is preferred. Glycerol can be introducedat any point during the process of the invention by any convenientmethod for combining the glycerol and/or formic acid with the componentsof the process. A preferred method for inclusion of glycerol and/orformic acid is by adding glycerol and/or formic acid to the aqueousbrine. When present, the amount of glycerol is preferably about 3 wt %to about 15 wt %, more preferably about 5 wt % to about 10 wt %,relative to the total weight of the composition. The amount of formicacid, when present, is typically about 500 ppm to about 5000 ppm,preferably about 750 ppm to about 3000 ppm, more preferably about 1000ppm to about 2500 ppm, relative to the total weight of the composition.It has been observed that the presence of glycerol inmanganese-containing aqueous brines of the invention may prevent orminimize precipitation in the aqueous brines, especially at pH values ofabout 3.5 or above.

In some preferred processes of this invention, only water, one or moreinorganic bromide salts, and one or more other water-soluble inorganicsalts are combined to form the zinc-free aqueous brines of thisinvention. In some of these preferred embodiments, the otherwater-soluble inorganic salts are selected from manganese(II) nitrateand a water-soluble polytungstate salt.

In some preferred processes of this invention, only water, one or moreinorganic bromide salts, one or more inorganic oxides and/or hydroxides,and/or hydrogen bromide and/or bromine are combined to form thezinc-free aqueous brines of this invention.

Preferred processes of this invention comprise combining, in any order,components comprising water and one or more inorganic bromide saltspreferably selected from the group consisting of calcium bromide,manganese(II) bromide, tin(II) bromide, tin(IV) bromide, bismuth(III)bromide, indium(III) bromide, and mixtures of any two or more of these;when calcium bromide is present, one or more other water-solubleinorganic salts, preferably selected from an inorganic bromide salt,manganese(II) nitrate, and a water-soluble polytungstate salt, is alsopresent. When bismuth(III) bromide is present, one or more otherwater-soluble inorganic salts, preferably selected from an inorganicbromide salt, is also present. Lithium bromide is used in combinationwith one or more alkali metal polytungstate salts. Manganese(II) bromideis preferably used in combination with one or more other water-solubleinorganic salts preferably selected from an inorganic bromide salt,manganese(II) nitrate, and a water-soluble polytungstate salt; inpreferred embodiments, the other inorganic salt is a bromide, and iscalcium bromide or a combination of calcium bromide and one or moreother inorganic bromide salts. When only one bromide salt is present,preferred inorganic bromide salts include tin(IV) bromide andindium(III) bromide, especially tin(IV) bromide. When two bromide saltsare used, they are preferably a combination of calcium bromide andmanganese(II) bromide; when three bromide salts are used, they arepreferably a combination of calcium bromide, manganese(II) bromide andtin(IV) bromide, or a combination of calcium bromide, manganese(II)bromide, and bismuth(III) bromide.

The composition formed has a density of about 14.3 ppg (1.71 kg/L) ormore, preferably of about 14.6 ppg (1.75 kg/L) or more; and a truecrystallization temperature of about 20° F. (−6.7° C.) or less,preferably about 10° F. (−12.2° C.) or less. An aqueous brine in whichthe only salt is manganese(II) bromide at a density of 15.0 ppg (1.80kg/L) has a true crystallization temperature of about −10.3° C. In someembodiments, the compositions formed preferably have densities of about14.8 ppg (1.77 kg/L) or more, or preferably about 15.0 ppg (1.80 kg/L)or more, or more preferably about 15.1 ppg (1.81 kg/L) or more. In otherembodiments, especially when the inorganic bromide salts are calciumbromide and another inorganic bromide selected from tin(IV) bromide,bismuth(III) bromide, or indium(III) bromide, the compositionspreferably have densities of about 16.0 ppg (1.92 kg/L) or more. When incombination with calcium bromide, the other inorganic bromide salt isusually in an amount of about 3.0 wt % to about 45 wt %, preferablyabout 5 wt % to about 40 wt %; more preferably about 6 wt % to about 35wt %, relative to the total weight of the composition formed. Whencalcium bromide is used in combination with manganese(II) nitrate, themanganese(II) nitrate is usually in the range of about 30 wt % to about75 wt %, sometimes preferably about 35 wt % to about 70 wt %, sometimespreferably about 10 wt % to about 50 wt %, relative to the total weightof the composition formed. When calcium bromide or manganese(II) bromideis used in combination with a water-soluble polytungstate salt, thewater-soluble polytungstate salt is typically in the range of about 5 wt% to about 40 wt %, preferably about 10 wt % to about 35 wt %, relativeto the total weight of the composition formed. When a combination oflithium bromide and one or more alkali metal polytungstate salts isused, the alkali metal polytungstate salt is generally in the range ofabout 5 wt % to about 40 wt %, preferably about 10 wt % to about 35 wt%, relative to the total weight of the composition formed.

In some preferred processes, the water, inorganic bromide salt(s) and,when used, one or more other water-soluble inorganic salts are combinedto form an aqueous solution. In other preferred processes, one or moreinorganic bromide salts are formed during the process from hydrogenbromide and/or bromine and an inorganic oxide and/or hydroxide. Theinorganic oxide and/or hydroxide is preferably selected from oxidesand/or hydroxides of calcium, manganese(II), tin(II), tin(IV),bismuth(III), indium(III), and mixtures of any two or more of theforegoing. When oxides and/or hydroxides of calcium are used, one ormore other water-soluble inorganic salts, preferably selected from aninorganic bromide salt, manganese(II) nitrate, and a water-solublepolytungstate salt, are also included. When oxides and/or hydroxides ofmanganese are used, they are preferably used in combination with one ormore other water-soluble inorganic salts preferably selected from aninorganic bromide salt, manganese(II) nitrate, and a water-solublepolytungstate salt. For lithium bromide in combination with awater-soluble polytungstate salt, lithium bromide can be formed fromlithium oxide and/or hydroxide with hydrogen bromide and/or bromine.

Preferred combinations of inorganic oxides and/or hydroxides are oxidesand/or hydroxides of manganese(II), tin(II), tin(IV), indium(III),and/or bismuth(III), in combination with calcium bromide or oxidesand/or hydroxides of calcium. Also preferred as the inorganic oxidesand/or hydroxides are combinations of calcium bromide or oxides and/orhydroxides of calcium with oxides and/or hydroxides of manganese(II);and/or tin(IV); combinations of calcium bromide or oxides and/orhydroxides of calcium with oxides and/or hydroxides of manganese(II) andoxides and/or hydroxides of tin(IV), or a combination of calcium bromidewith oxides and/or hydroxides of manganese(II) bromide and oxides and/orhydroxides bismuth(III) bromide. When only one inorganic bromide salt ispresent, preferred inorganic oxides and/or hydroxides are oxides and/orhydroxides of tin(IV), and oxides and/or hydroxides of indium(III),especially oxides and/or hydroxides of tin(IV).

Optionally, the processes further comprise heating the aqueous brineduring and/or after combining the components; temperatures andpreferences therefor are as described above.

These preferred processes can further comprise adjusting the pH to avalue in the range of about 1 to about 7 by adding an acid and/or aninorganic oxide and/or hydroxide to the aqueous brine composition;preferably, the inorganic oxide and/or hydroxide is an oxide and/orhydroxide of calcium, manganese(II), or tin(II), tin(IV), bismuth(III),indium(III), or mixtures of any two or more of these. Preferred pHranges are as described above.

Naturally-occurring manganese is present in manganese nodules, moreaccurately called polymetallic nodules, on the seabed. These nodules areformed in oceans throughout the world, and the most abundant metals inthese nodules are manganese and iron.

The following examples are presented for purposes of illustration, andare not intended to impose limitations on the scope of this invention.

In the following Examples, the densities of the solutions weredetermined by the oscillating U-tube technique, which measures thefrequency of the oscillation of the liquid sample.

True crystallization temperature determinations in the Examples weredetermined by one of the two the procedures described here.

Classical Procedure.

A jacketed glass tube containing 50 mL of sample was mechanicallystirred while being cooled using a recirculating bath containing acooling fluid (for example, glycol). When the sample reached atemperature about 10° C. above the expected first crystal to appear(FCTA) temperature, the sample was cooled at a rate of approximately0.5° C./min. or a smaller temperature increment until the TCT (truecrystallization temperature) is observed. The FCTA temperature wasrecorded at the lowest temperature reached before precipitation, and theTCT was recorded at the highest temperature achieved immediately afterprecipitation started. The sample was removed from the recirculatingbath and warmed; when all of the precipitate had disappeared, the lastcrystal to dissolve (LCTD) temperature was recorded. Each determinationwas run with a seed crystal of silica (≤50 μm, ˜0.03 g) in the sample.

Instrument Procedure.

A sample cup containing 0.25 mL of the sample was placed in a Cloud,Pour, and Freeze Point Lab Analyzer (model no. 70Xi; Phase Technology,Richmond, Canada), and the sample was cooled at 0.5 degrees Celsius perminute until freezing was detected by diffusive light-scattering.

Comparative Example 1

Measurements of the true crystallization temperature (TCT) were made onthree samples of calcium bromide aqueous solutions. These samplescontained only water and calcium bromide. Results are summarized inTable 1 below.

Comparative Example 2

Two samples were prepared starting from 50.0 g of an aqueous CaBr₂solution having a density of 14.2 ppg (1.70 kg/L). To one sample moreCaBr₂ (4.32 g) was added; to the other sample, ZnBr₂ (3.19 g) was added.Results are summarized in Table 1 below.

Comparative Example 3

Two samples were prepared starting from 40.0 g of an aqueous CaBr₂solution having a density of 12.8 ppg (1.53 kg/L). To one sample moreCaBr₂ (13.18 g) was added; to the other sample, ZnBr₂ (11.90 g) wasadded. Results are summarized in Table 1 below.

Comparative Example 4

A series of samples was prepared starting from 50.0 g of an aqueousCaBr₂ solution having a density of 14.2 ppg (1.70 kg/L). The salts LiBr(4.18 g), SrBr₂.6H₂O (7.01 g), and BaBr₂ (2.21 g) were added to separateCaBr₂ solutions. Testing of the strontium-containing andbarium-containing samples was discontinued due to solubility and densityissues.

Another series of samples was prepared, starting from 40.0 g of anaqueous CaBr₂ solution having a density of 12.8 ppg (1.53 kg/L). Thesalts LiBr (15.18 g), and MgBr₂.6H₂O were added to separate CaBr₂solutions. Testing of the magnesium-containing sample was discontinueddue to solubility and density issues. Results are summarized in Table 1below.

TABLE 1 Non-CaBr₂ Total Compar. Inorganic bromide bromide Ex. Runbromides amount^(a) amount^(a) Density TCT^(b) 1 a CaBr₂ none 56.3 wt %14.76 ppg (1.769 kg/L) 35.6° F. (2.0° C.) b CaBr₂ none 56.0 wt % 14.68ppg (1.759 kg/L) 32.9° F. (0.5° C.) c CaBr₂ none 55.4 wt % 14.58 ppg(1.747 kg/L) 24.8° F. (−4.0° C.) 2 a CaBr₂ none 56.9 wt % 14.54 ppg(1.742 kg/L) 22.1° F. (−5.5° C.) b CaBr₂,  6.0 wt % 56.0 wt % 14.57 ppg(1.746 kg/L) <−5.8° F. (<−21.0° C.) ZnBr₂ 3 a CaBr₂ none 58.5 wt % 14.63ppg (1.753 kg/L) 26.6° F. (−3.0° C.) b CaBr₂, 22.9 wt % 57.5 wt % 14.67ppg (1.757 kg/L) <−5.8° F. (<−21.0° C.) ZnBr₂ 4 a CaBr₂,  7.7 wt % 56.8wt % 14.55 ppg (1.743 kg/L) 33.8° F. (1.0° C.) LiBr b CaBr₂, 27.5 wt %66.1 wt % 14.60 ppg (1.749 kg/L) 39.2° F. (4.0° C.) LiBr ^(a)Relative tototal weight of solution. ^(b)True crystallization temperature;determined by the classical procedure.

Example 1

A sample was prepared starting from 50.0 g of an aqueous CaBr₂ solutionhaving a density of 14.2 ppg (1.70 kg/L). MnBr₂ (3.27 g) was added tothe CaBr₂ solution. Results are summarized in Table 2 below.

Example 2

A sample was prepared starting from 40.0 g of an aqueous CaBr₂ solutionhaving a density of 12.8 ppg (1.53 kg/L). MnBr₂ (10.18 g) was added tothe CaBr₂ solution. Results are summarized in Table 2 below.

Example 3

Five separate samples were prepared by adding an amount of MnBr₂ toaqueous CaBr₂ solutions of densities ranging from 13.4 to 14.0 ppg (1.61to 1.68 kg/L) to obtain aqueous brines with densities of about 14.6 to15.1 ppg (1.75 to 1.81 kg/L). Some of the samples were filtered toremove haziness. All of the samples were then analyzed to determinetheir density and true crystallization temperature (TCT). Results aresummarized in Table 2 below.

Example 4

Into a 500 ml flask was placed 160 grams of a CaBr₂ solution having adensity of 14.2 ppg (1.70 kg/L). The solution was heated to 60° C. andthen 30 grams of SnBr₂ powder was added with stirring. After stirringfor about 1 hour at 60° C., all of the SnBr₂ had dissolved, to give ahazy light tan solution. The solution was cooled to ambient temperatureand then vacuum filtered through a 1 micron filter medium, to give aclear colorless solution having a density of 16 ppg (1.9 kg/L). To aportion (about 90 g) of this solution, deionized water (9 g) was addedto give, after mixing, a solution with a density of 15 ppg (1.8 kg/L).Both samples were stored in a 6 to 7° F. (−14.4 to −13.9° C.) freezerovernight, and after 24 hours remained clear and colorless with noprecipitate. Results are summarized in Table 2 below.

Example 5

Into a 3 L jacketed round-bottom flask equipped with a mechanicalstirrer, a thermocouple, and an addition funnel was charged aqueousCaBr₂ (14.2 ppg; 673.68 g), deionized water (126.32 g), and MnO powder(99 wt %, 67.92 g). While mixing, this slurry was heated at 67° C., andaqueous HBr (48 wt %; 320.96 g) was added over 1 hour via the additionfunnel. After holding at 67° C. for 40 minutes, aqueous NaOH (50 wt %)or aqueous HBr (48 wt %) was used to titrate the pH to 4.89; some solidformation was observed. The total amount of HBr and/or NaOH solutionadded was less than 10 g. After cooling to room temperature, the mixturewas filtered under vacuum, more aqueous HBr (48 wt %) was added toadjust the pH to 3.0 to 3.5. A total of 2.04 g of NaOH solution wasadded; less than 5 g of aqueous HBr were added. Water (159 g) wasremoved under weak vacuum at 54° C. to give a clear pink solution (1004g) with a density of 1.78 g/mL (14.8 ppg) and a pH of 3.4. Results aresummarized in Table 2 below.

Example 6

Into a 3 L jacketed round-bottom flask equipped with a mechanicalstirrer, a thermocouple, and an addition funnel was charged aqueousCaBr₂ (14.2 ppg; 673.68 g), deionized water (126.32 g), and MnO powder(99 wt %, 67.92 g). While mixing, this slurry was heated at 67° C. andaqueous HBr (48 wt %; 320.96 g) was added over 1 hour via the additionfunnel. After holding at 67° C. for 35 minutes, aqueous HBr (48 wt %;0.12 g) was added to titrate the pH to 3.18; some solid formation wasobserved. After cooling to room temperature, the mixture was filteredunder vacuum. Water (165.6 g) was removed under weak vacuum at 54° C. togive a clear pink solution (1010 g) with a density of 1.78 g/mL (14.9ppg) and a pH of 3.03. Results are summarized in Table 2 below.

TABLE 2 Non-CaBr₂ Total Inorganic bromide bromide Ex. Run bromidesamount^(a) amount^(a) Density TCT^(b) 1 — CaBr₂, 6.1 wt % 56.1 wt %14.76 ppg (1.769 kg/L) 10.4° F. (−12.0° C.) MnBr₂ 2 — CaBr₂, 20.3 wt %56.0 wt % 14.63 ppg (1.753 kg/L) <−13° F. (−25° C.) MnBr₂ 3 a CaBr₂, 9.3wt % 56.5 wt % 14.89 ppg (1.784 kg/L) <−7.6° F. (−22° C.) MnBr₂ b CaBr₂,14.4 wt % 56.5 wt % 15.01 ppg (1.799 kg/L) −9.4° F. (−23.0° C.) MnBr₂ cCaBr₂, 13.6 wt % 55.3 wt % 15.10 ppg (1.809 kg/L) 7.7° F. (−13.5° C.)MnBr₂ d CaBr₂, 13.6 wt % 57.6 wt % 14.67 ppg (1.758 kg/L) <−13° F (−25°C.) MnBr₂ e CaBr₂, 20.1 wt % 57.2 wt % 14.63 ppg (1.753 kg/L) <−13° F.(−25° C.) MnBr₂ 4 a CaBr₂, 15.8 wt % 60.6 wt % 16 ppg (1.9 kg/L) low^(c)SnBr₂ b CaBr₂, 6.4 wt % 47.1 wt % 15 ppg (1.8 kg/L) low^(c) SnBr₂ 5 —CaBr₂, 20.0 wt %^(d) 55.7 wt % 14.8 ppg (1.78 kg/L) −14.8° F. (−26° C.)MnO/HBr 6 — CaBr₂, 20.1 wt %^(d) 55.6 wt % 14.9 ppg (1.78 kg/L) −13° F.(−25° C.) MnO/HBr ^(a)Relative to total weight of solution. ^(b)Truecrystallization temperature; determined by the classical procedure.^(c)Below the temperature of the freezer (6 to 7° F.; −14.4 to −13.9°C.); no precipitate had formed in the samples after 1 week in thefreezer. ^(d)Calculated as MnBr₂.

Example 7

Several CaBr₂/MnBr₂ aqueous brine samples with different pH values wereprepared starting from a CaBr₂/MnBr₂ aqueous brine prepared as inExample 5. The pH value of each sample was adjusted by adding aqueousHBr (48 wt %) and/or aqueous NaOH (50%) until the desired pH value wasreached. In each sample, the total amount of HBr and/or NaOH solutionadded was less than 5 g. Some of the samples to which NaOH was addedformed a small amount of precipitate; these samples were filtered. Thesesamples with different pH values were placed in a 60° C. oven toheat-age for one week. The turbidity and presence or absence of aprecipitate were observed visually and recorded at the end of the week.Results are summarized in Table 3 below.

Example 8

Several CaBr₂/MnBr₂ aqueous brine samples with different pH values wereprepared starting from a CaBr₂/MnBr₂ aqueous brine prepared as inExample 5. The pH value of each sample was adjusted by adding aqueousHBr (48 wt %) and/or aqueous NaOH (50%) until the desired pH value wasreached. In each sample, the total amount of HBr and/or NaOH solutionadded was less than 10 g. Some of the samples to which NaOH was addedformed a small amount of precipitate; these samples were filtered. Tosome of the samples, enough glycerol was added to make a solutioncontaining either 5 wt % or 10 wt % glycerol. These samples were placedin a 60° C. oven to heat-age for one week. The turbidity and presence orabsence of a precipitate were observed visually and recorded at the endof the week. Results are summarized in Table 3 below.

Example 9

Example 8 was repeated, except that the samples were allowed to sit atambient temperature rather than oven-aging. Results are summarized inTable 3 below.

Example 10

Several CaBr₂/MnBr₂ aqueous brine samples having a pH of about 3.5 orless as in Example 5 were used. To these samples, enough glycerol wasadded to make a solution containing either 5 wt % or 10 wt % glycerol.All of these solutions remained clear; no precipitate was observed inany of the solutions over time at room temperature.

TABLE 3 Inorganic Glycerol Aging Ex. bromides amt.^(a) pH TurbidityPrecip. temp. 7 CaBr₂, 0 1.00 clear none 60° C. MnBr₂ 1.99 clear none3.00 clear none 3.16 clear none 3.30 clear none 3.40 clear none 3.62cloudy none 3.99 cloudy yes 4.28 cloudy yes 8 CaBr₂, 0 4.58 cloudy yes60° C. MnBr₂ 5% 4.58 cloudy none 0 4.28 cloudy yes 5% 4.28 clear none10%  4.28 clear none 9 CaBr₂, 0 4.58 cloudy yes ambient MnBr₂ 5% 4.58clear none 0 4.28 cloudy yes 5% 4.28 clear none 10%  4.28 clear none^(a)Relative to total weight of solution.

Example 11

A sample was prepared starting from 100.0 g of an aqueous CaBr₂/MnBr₂(1.75:1 (wt:wt) CaBr₂:MnBr₂) clear brine fluid having a density of 15.0ppg (1.80 kg/L). SnBr₂ (7.00 g) was mixed with the CaBr₂/MnBr₂ clearbrine fluid at 48° C. After the solids had dissolved, the mixture wascooled to room temperature and then vacuum filtered through a 2 micronglass filter, to give a clear liquid having a density of 15.8 ppg (1.89kg/L). Some of the water was removed under vacuum at 54° C. to give aclear brine fluid with a density of 16.0 ppg (1.92 kg/L). A sample ofthis clear brine fluid was analyzed to determine its truecrystallization temperature (TCT), which was below −23° C. Results aresummarized in Table 4 below.

In Examples 12, 13, 14, 15 and 16, the densities were measured withcalibrated graduated cylinders. In this method, a 50 mL graduatedcylinder was calibrated using 30.000 g of deionized water. The volume(29.7 mL) was recorded to calibrate the scale on the graduated cylinder.Each well fluid sample (29.7 mL) was weighed, and the density wascalculated by using the following formula: density (g/mL)=mass (g)/29.7mL. For smaller sample sizes, a 10 mL graduated cylinder was calibratedand used in the same manner to determine the densities.

Example 12

Several samples were prepared by mixing an amount of either SnBr₄ (4.00g; 9.00 g) or BiBr₃ (4.00 g; 6.00 g) with 27.00 g of an aqueousCaBr₂/MnBr₂ (1.75:1 (wt:wt) CaBr₂:MnBr₂) clear brine fluid having adensity of 14.8 ppg (1.77 kg/L). All of the samples were then analyzedto determine their density. Each sample was filtered through a 1 micronsyringe filter, and a portion of each sample was placed in a freezer at−16° C., and another portion of each sample was placed in an oven at 60°C. All of the samples in both the oven and the freezer remained clearafter 3 days or longer. Results are summarized in Table 4 below.

TABLE 4 Non-CaBr₂ Total Inorganic bromide MnBr₂ bromide Soln, remainedEx. Run bromides amount^(a) amount^(a) amount^(a) Density clear at −16°C. 11 — CaBr₂, 26.3 wt % 19.6 wt % 60.6 wt % 16.0 ppg (1.92 kg/L) atleast one week MnBr₂, SnBr₂ 12 a CaBr₂, 30.6 wt % 17.7 wt % 61.5 wt %16.1 ppg (1.93 kg/L) at least one week^(b) MnBr₂, SnBr₄ b CaBr₂, 40.3 wt% 15.3 wt % 66.9 wt % 17.5 ppg (2.10 kg/L) at least 3 days^(c) MnBr₂,SnBr₄ c CaBr₂, 34.9 wt % 16.7 wt % 64.0 wt % 16.7 ppg (2.00 kg/L) atleast one day MnBr₂, SnBr₄ d CaBr₂, 30.6 wt % 17.7 wt % 61.5 wt % 16.3ppg (1.95 kg/L) at least one week^(c) MnBr₂, BiBr₃ e CaBr₂, 41.0 wt %20.7 wt % 61.5 wt % 16.5 ppg (1.98 kg/L) at least one week MnBr₂, BiBr₃^(a)Relative to total weight of solution. ^(b)True crystallizationtemperature −34.95° C.; determined by the instrument procedure. ^(c)Truecrystallization temperature below −32° C.; determined by the instrumentprocedure.

Example 13

Two samples were prepared by mixing an amount of SnBr₂ (1.30 g; 4.00 g)with 27.00 g of an aqueous CaBr₂/MnBr₂ (1.75:1 (wt:wt) CaBr₂:MnBr₂)clear brine fluid having a density of 15.3 ppg (1.83 kg/L). Both of thesamples were then analyzed to determine their density. Each sample wasfiltered through a 1 micron syringe filter, then enough formic acid tomake a concentration of 2000 ppm in the solution was added. Then aportion of each sample was placed in a freezer at −16° C., and anotherportion of each sample was placed in an oven at 60° C. The samples inboth the oven and the freezer remained clear after one week. Results aresummarized in Table 5 below.

Example 14

Two separate samples were prepared by mixing either SnBr₂ (6.00 g) orBiBr₃ (6.00 g) with an aqueous CaBr₂ solution containing formic acid(2000 ppm) and having a density of 14.2 ppg (1.70 kg/L). Both of thesamples were then analyzed to determine their density. Each sample wasfiltered through a 1 micron syringe filter, then enough formic acid tomake a concentration of 2000 ppm in the solution was added. Then aportion of each sample was placed in a freezer at −16° C., and anotherportion of each sample was placed in an oven at 60° C. The samples inboth the oven and the freezer remained clear overnight or longer.Results are summarized in Table 5 below.

TABLE 5 Non-CaBr₂ Total Inorganic bromide MnBr₂ bromide Soln, remainedEx. Run bromides amount^(a) amount^(a) amount^(a) Density clear at −16°C. 13 a CaBr₂, 24.0 wt % 19.4 wt % 57.9 wt % 15.9 ppg (1.90 kg/L) atleast one week MnBr₂, SnBr₂ b CaBr₂, 30.6 wt % 17.7 wt % 61.5 wt % 16.3ppg (1.95 kg/L) at least one week MnBr₂, SnBr₂ 14 a CaBr₂, 18.2 wt %none 61.7 wt % 16.2 ppg (1.94 kg/L) at least overnight SnBr₂ b CaBr₂,18.2 wt % none 61.7 wt % 16.6 ppg (1.99 kg/L) at least 2 days BiBr₃^(a)Relative to total weight of solution.

Example 15

Several samples were prepared by mixing an amount of one or moreinorganic bromide salts, and in some instances deionized water andformic acid, with an amount of an aqueous calcium bromide solutionhaving a density of 14.2 ppg (1.70 kg/L; WellBrom®, AlbemarleCorporation). Each mixture was heated to dissolve the solids. Detailsfor each solution are as follows:

-   -   formic acid (80.0 mg) and InBr₃ (6.00 g); deionized water        (0.50 g) had been added to 27.00 g of the calcium bromide        solution; heating was at 50° C.;    -   InBr₃ (6.90 g) and 27.00 g of the calcium bromide solution;        heating was at 48 to 50° C.;    -   an aqueous solution of MnBr₂ (14.10 g; 50.3 wt %) and InBr₃        (6.96 g); 13.15 g of the calcium bromide solution; heating was        at 48 to 50° C.; and    -   formic acid (80.0 mg) and SnBr₄ with 27.00 g of the calcium        bromide solution, to which deionized water (0.73 g) had been        added; heating was at 49° C.

After the solids had dissolved, the mixture was cooled to roomtemperature. After cooling to room temperature, each solution wasanalyzed to determine its density. A sample from each solution wasplaced in a freezer at −16° C., and another sample from each solutionwas placed in an oven at 60° C. Results are summarized in Table 6 below.

Example 16

A sample was prepared by mixing SnBr₄ (10.17 g) and deionized water(4.11 g) containing HBr (0.02 g; 48%). The mixture was heated at 35° C.to dissolve the solids. After the solids had dissolved, the mixture wascooled to room temperature, yielding a clear liquid having a density of18.8 ppg (2.25 kg/L). A sample from the solution was placed in a freezerat −16° C., and another sample from the solution was placed in an ovenat 60° C. The samples in both the oven and the freezer remained clearafter 72 hours. Results are summarized in Table 6 below.

Example 17

A sample was prepared by mixing InBr₃ and deionized water in amounts toform a clear solution having a density of 16.0 ppg (1.92 kg/L), a sampleof which was placed in a freezer at −16° C. Results are summarized inTable 6 below.

TABLE 6 Non-CaBr₂ Total Inorganic bromide bromide Formic Soln, remainedEx. Run bromide(s) amount^(a) amount^(a) acid^(a) Density clear at −16°C. 15 a CaBr₂, 17.9 wt % 60.8 wt % 2280 ppm 16.0 ppg (1.92 kg/L) atleast 6 days InBr₃ b CaBr₂, 36.6 wt % 64.9 wt % none 17.2 ppg (2.06kg/L) at least 72 hrs.^(b) MnBr₂, InBr₃ c CaBr₂, 41.0 wt % 61.5 wt %none 16.6 ppg (1.99 kg/L) at least 96 hrs. MnBr₂, InBr₃ d CaBr₂, 24.5 wt% 63.7 wt % 2700 ppm 16.5 ppg (1.98 kg/L) at least 6 days SnBr₄ 16 —SnBr₄ 71.1 wt % 71.1 wt % none 18.8 ppg (2.25 kg/L) at least 72 hrs. 17— InBr₃   60 wt %   60 wt % none 16.0 ppg (1.92 kg/L) at least 24 hrs.^(a)Relative to total weight of solution. ^(b)True crystallizationtemperature below −32° C.; determined by the instrument procedure.

Example 18

Several samples were prepared by dissolving an amount of Mn(NO₃)₂.H₂O indeionized water at ambient temperature, adding CaBr₂ to the solution,and in some instances also adding HNO₃ or HCl. Each mixture was heatedto dissolve the solids. Details for each solution are as follows:

-   a) Mn(NO₃)₂.H₂O (24.4 g) and deionized water (10.70 g), CaBr₂    (20.45 g) added at 56° C.;-   b) Mn(NO₃)₂.H₂O (12.20 g) and deionized water (5.35 g), CaBr₂ (10.23    g), HNO₃ (conc., 65 mg) was then added;-   c) Mn(NO₃)₂.H₂O (12.20 g) and deionized water (2.09 g), CaBr₂ (5.02    g);-   d) Mn(NO₃)₂.H₂O (12.20 g) and deionized water (5.35 g), then added    HCl (conc.; 58 mg), then CaBr₂ (10.23 g).

After the solids had dissolved, each mixture was cooled to roomtemperature. The cooled solutions were clear. After cooling to roomtemperature, each sample was filtered through a 1 micron syringe filterand analyzed to determine its density. A portion of each sample wasplaced in a freezer at −16° C. All of the samples in the freezerremained crystal-free for at least one week. Results are summarized inTable 7 below.

Example 19

A sample was prepared by adding Mn(NO₃)₂.H₂O (3.00 g) to an aqueousCaBr₂ solution (57.6 wt %, 25.05 g). The mixture was heated to 50° C.and then cooled to room temperature to give a clear, light pink solutionwith a density of 15.3 ppg (1.83 kg/L). After filtration through a1-micron syringe filter, a portion of the sample was placed in a freezerat −16° C., and another portion of the sample was placed in an oven at60° C. Both samples remain clear after 24 hours. Results are summarizedin Table 7 below.

TABLE 7 Total Total Inorganic bromide Mn(NO₃)₂ Soln, remained Ex. Runbromide amount^(a) amount^(a) Acid Density clear at −16° C. 18 a CaBr₂36.8 wt % 43.9 wt % — 14.9 ppg (1.79 kg/L) at least one week 18 b CaBr₂36.7 wt % 43.8 wt % HNO₃ 14.9 ppg (1.79 kg/L) at least one week 18 cCaBr₂ 26.0 wt % 57.2 wt % — 15.1 ppg (1.81 kg/L) at least one week 18 dCaBr₂ 36.7 wt % 39.7 wt % HCl 15.0 ppg (1.80 kg/L) at least one week 19— CaBr₂ 51.4 wt % 10.7 wt % — 15.3 ppg (1.83 kg/L) at least 24 hrs.^(a)Relative to total weight of solution.

Example 20

Several samples were prepared by diluting an aqueous solution of eitherCaBr₂ or MnBr₂ with deionized water and adding an amount of sodiummetatungstate to the diluted solution at ambient temperature. Eachmixture was then heated. Details for each solution are as follows:

-   a) CaBr₂ (aq., 53.2 wt %, 15.05 g), deionized water (2.81 g), sodium    metatungstate hydrate (4.50 g); heating was at 54-56° C.;-   b) MnBr₂ (aq., 50 wt %, 15.00 g), deionized water (2.00 g), sodium    metatungstate hydrate (3.29 g); heating was at 35° C.;-   c) MnBr₂ (aq., 50 wt %, 15.00 g), deionized water (2.00 g), sodium    metatungstate hydrate (6.00 g); heating was at 50 to 58° C.

After the solids had dissolved, each mixture was cooled to roomtemperature. After cooling to room temperature, each sample was filteredthrough a 1 micron syringe filter, and clear, colorless solutions wereobtained. Each sample was then analyzed to determine its density. Aportion of each sample was placed in a freezer at −16° C. All of thesamples in the freezer remained clear at least overnight. Results aresummarized in Table 8 below.

Example 21

Two samples were prepared by mixing an amount of lithium bromide with ametatungstate salt. Details for each solution are as follows:

-   A) LiBr (8.00 g) was dissolved in deionized water (12.04 g). Into    this solution was added sodium metatungstate hydrate (8.33 g), to    give a colorless solution with a density of 15.0 ppg (1.80 kg/L);    and-   B) LiBr (10.00 g) was dissolved in deionized water (10.00 g). Into    this solution was added an aqueous lithium metatungstate solution    (p=2.95 g/mL) to give a colorless solution with density of 16.3 ppg    (1.95 kg/L).

Each solution was filtered through a 1-micron syringe filter, afterwhich a portion of each sample was placed in a freezer at −16° C., andanother portion of each sample was placed in an oven at 60° C. Both thefreezer and oven samples from run A remained clear after one week. Boththe freezer and oven samples from run B remained clear after at least 20hours. Results are summarized in Table 8 below.

TABLE 8 Total Total Inorganic bromide metatungstate Ex. Run bromideamount^(a) salt amount^(a) Density TCT^(b) 20 a CaBr₂ 35.8 wt % 20.0 wt% 14.9 ppg (1.79 kg/L) −27.8° C. 20 b MnBr₂ 37.0 wt % 18.8 wt % 15.3 ppg(1.83 kg/L) —^(c) 20 c MnBr₂ 32.6 wt % 25.9 wt % 16.4 ppg (1.97 kg/L)−31.0° C. 21 A LiBr 28.2 wt % 29.4 wt % 15.0 ppg (1.80 kg/L) −29.8° C.21 B LiBr 16.3 ppg (1.95 kg/L) —^(d) ^(a)Relative to total weight ofsolution. ^(b)True crystallization temperature; determined by theinstrument procedure. ^(c)Solution remained clear at −16° C. overnight.^(d)Solution remained clear at −16° C. for at least 20 hours.

Components referred to by chemical name or formula anywhere in thespecification or claims hereof, whether referred to in the singular orplural, are identified as they exist prior to coming into contact withanother substance referred to by chemical name or chemical type (e.g.,another component, a solvent, or etc.). It matters not what chemicalchanges, transformations and/or reactions, if any, take place in theresulting mixture or solution as such changes, transformations, and/orreactions are the natural result of bringing the specified componentstogether under the conditions called for pursuant to this disclosure.Thus the components are identified as ingredients to be brought togetherin connection with performing a desired operation or in forming adesired composition. Also, even though the claims hereinafter may referto substances, components and/or ingredients in the present tense(“comprises”, “is”, etc.), the reference is to the substance, componentor ingredient as it existed at the time just before it was firstcontacted, blended or mixed with one or more other substances,components and/or ingredients in accordance with the present disclosure.The fact that a substance, component or ingredient may have lost itsoriginal identity through a chemical reaction or transformation duringthe course of contacting, blending or mixing operations, if conducted inaccordance with this disclosure and with ordinary skill of a chemist, isthus of no practical concern.

The invention may comprise, consist, or consist essentially of thematerials and/or procedures recited herein.

As used herein, the term “about” modifying the quantity of an ingredientin the compositions of the invention or employed in the methods of theinvention refers to variation in the numerical quantity that can occur,for example, through typical measuring and liquid handling proceduresused for making concentrates or use solutions in the real world; throughinadvertent error in these procedures; through differences in themanufacture, source, or purity of the ingredients employed to make thecompositions or carry out the methods; and the like. The term about alsoencompasses amounts that differ due to different equilibrium conditionsfor a composition resulting from a particular initial mixture. Whetheror not modified by the term “about”, the claims include equivalents tothe quantities.

Except as may be expressly otherwise indicated, the article “a” or “an”if and as used herein is not intended to limit, and should not beconstrued as limiting, the description or a claim to a single element towhich the article refers. Rather, the article “a” or “an” if and as usedherein is intended to cover one or more such elements, unless the textexpressly indicates otherwise.

This invention is susceptible to considerable variation in its practice.Therefore the foregoing description is not intended to limit, and shouldnot be construed as limiting, the invention to the particularexemplifications presented hereinabove.

That which is claimed is:
 1. A wellbore fluid comprising a zinc-freeaqueous brine having a density of 1.71 kg/L (14.3 pounds per gallon) to2.28 kg/L (19.0 pounds per gallon), and a true crystallizationtemperature of −6.7° C. (20° F.) or less, which aqueous brine comprisescalcium bromide and a manganese salt selected from manganese(II)bromide, manganese(II) nitrate, and manganese polytungstate.
 2. Thewellbore fluid of claim 1 wherein the manganese salt is manganese(II)bromide.
 3. The wellbore fluid of claim 1 in which the aqueous brine hasa density of 1.75 kg/L (14.6 pounds per gallon) or more.
 4. The wellborefluid of claim 2 in which the aqueous brine has a density of 1.75 kg/L(14.6 pounds per gallon) or more and a pH value in the range of 2.5 to5.
 5. The wellbore fluid of claim 2 also comprising tin(IV) bromide,wherein the aqueous brine has a density of 1.80 kg/L (15.0 pounds pergallon) or more.
 6. The wellbore fluid of claim 2 also comprisingbismuth(III) bromide, and wherein the aqueous brine has a density of1.92 kg/L (16.0 pounds per gallon) or more.
 7. The wellbore fluid ofclaim 2 also comprising tin(II) bromide or indium(III) bromide.
 8. Thewellbore fluid of claim 2 which also comprises tin(II) bromide, whereinthe aqueous brine has a density of 1.80 kg/L (15.0 pounds per gallon) ormore; or indium(III) bromide, wherein the aqueous brine has a density of1.92 kg/L (16.0 pounds per gallon) or more.
 9. A process for forming awellbore fluid comprising a zinc-free aqueous brine having a density of1.71 kg/L (14.3 pounds per gallon) to 2.28 kg/L (19.0 pounds pergallon), and a true crystallization temperature of −6.7° C. (20° F.) orless, which process comprises mixing, in any order, componentscomprising water, calcium bromide and a manganese salt selected frommanganese(II) bromide, manganese(II) nitrate, and manganesepolytungstate.
 10. The process of claim 9 wherein the manganese salt ismanganese(II) bromide.
 11. The process of claim 9 in which the aqueousbrine has a density of 1.75 kg/L (14.6 pounds per gallon) or more. 12.The process of claim 10 in which the aqueous brine has a density of 1.75kg/L (14.6 pounds per gallon) or more and a pH value in the range of 2.5to
 5. 13. The process of claim 10 wherein the aqueous brine alsocomprises tin(IV) bromide, wherein the aqueous brine has a density of1.80 kg/L (15.0 pounds per gallon) or more.
 14. The process of claim 10wherein the aqueous brine also comprises bismuth(III) bromide, andwherein the aqueous brine has a density of 1.92 kg/L (16.0 pounds pergallon) or more.
 15. The process of claim 10 wherein the aqueous brinealso comprises tin(II) bromide or indium(III) bromide.
 16. The processof claim 10 wherein the aqueous brine also comprises tin(II) bromide,wherein the aqueous brine has a density of 1.80 kg/L (15.0 pounds pergallon) or more; or indium(III) bromide, wherein the aqueous brine has adensity of 1.92 kg/L (16.0 pounds per gallon) or more.
 17. A method oftreating a wellbore, said method comprising: introducing into thewellbore a wellbore fluid comprising a zinc-free aqueous brine having adensity of 1.71 kg/L (14.3 pounds per gallon) to 2.28 kg/L (19.0 poundsper gallon), and a true crystallization temperature of −6.7° C. (20° F.)or less, which fluid comprises calcium bromide and a manganese saltselected from manganese(II) bromide, manganese(II) nitrate, andmanganese polytungstate.
 18. The method of claim 17 wherein themanganese salt is manganese(II) bromide.
 19. The method of claim 17 inwhich the aqueous brine has a density of 1.75 kg/L (14.6 pounds pergallon) or more.
 20. The method of claim 18 in which the aqueous brinehas a density of 1.75 kg/L (14.6 pounds per gallon) or more and a pHvalue in the range of 2.5 to
 5. 21. The method of claim 18 wherein theaqueous brine also comprises tin(IV) bromide, and wherein the aqueousbrine has a density of 1.80 kg/L (15.0 pounds per gallon) or more. 22.The method of claim 18 wherein the aqueous brine also comprisesbismuth(III) bromide, and wherein the aqueous brine has a density of1.92 kg/L (16.0 pounds per gallon) or more.
 23. The method of claim 18wherein the aqueous brine also comprises tin(II) bromide or indium(III)bromide.
 24. The method of claim 18 wherein the aqueous brine alsocomprises tin(II) bromide, wherein the aqueous brine has a density of1.80 kg/L (15.0 pounds per gallon) or more; or indium(III) bromide,wherein the aqueous brine has a density of 1.92 kg/L (16.0 pounds pergallon) or more.